It is known to use non-linear, computer-based editing systems to edit motion picture media such as digitized video or film. Generally, motion picture media is first digitized and stored on the system as source media. The editor then uses the editing system, which can employ a timeline metaphor, to develop a composition made up of clips from the source media. These types of editing systems have greatly increased the efficiency of the editing process, and have allowed editors to concentrate on the creative rather than mechanical aspects of editing.